Microwave switch



April 18, 1961 J. c. ROLFS MICROWAVE SWITCH Filed Jan. 19, 1960 INVENTOR. JOHN C. ROLFS N ATTORNEY.

2,980,869 MICROWAVE SWITCH John C. Rolfs, White Plains, -N.Y., assignor to General Precision, Inc., a corporation of Delaware Filed Jan. 19, 1960, Ser. No. 3,294

2 Claims. (Cl. 3337) This invention relates to microwave switches and particularly to phase-reversing microwave switches.

An example of the use of such switches is in beamshifting microwave antennas. One form of such antenna consists of a number of elemental radiators arranged in a plane and having two microwave input terminals. When these terminals arefed with inphase microwave energy two beams are radiated by the antenna in two selected directions. The switch for such an antenna should reverse the phase of one of the feeds accurately and rapidly, and should be. low-loss during transition from one position to the other; Since the beam directions of such an antenna are highly sensitive to the phases of the inputs, the phases must be controlled with great accuracy.

The present invention provides such a switch. Because the switch is electronic, its speed is limited only by the electrical time constant of its actuating circuit. The loss during switching, as indicated by change of the voltage standing wave ratio, is so small as to be unmeasurable, and either the phases or the amplitudes of the outputs can be matched as closely as may be desired. The invention provides a turnstile junction combined with a particular form of microwave polarization rotator. The arms of the turnstile junction'are short circuited at selected points.

The turnstile junction is described in volume 8 of the Radiation Laboratory Series, entitled Principles of Microwave Circuits, by Montgomery et al., on page 459. A form of rotator is described in US. Patent No. 2,719,274.

In the operation of the apparatus of this invention the polarization rotator serves as the microwave input to the round waveguide of the turnstile junction and two unshorted turnstile junction arms constitute the two outputs. When the rotator is not excited the phases of the outputs, are opposite, and when the rotator is excited so that it rotates the input polarization by 90, the output phases are alike.

, One purpose of this invention'is to provide a switch for changing the phase difference of two microwave energies by 180.

Another purpose ofthis invention is to provide a switch having no moving parts which changes the relative phases of two microwave outputs from the same to opposed phases. v

Still another purpose of this invention is to provide a phase-reversing switch having no increased loss during the switching transition. I

Still another purpose of this invention is to provide a phase-reversing switch which converts any input phase error into an output amplitude error.

, A further understandingjof this invention may besecured fronrthe detaileddescription and the drawing inv Wwhi ch the single figure illustrates an embodiment of the tent 2,980,869 Patented Apr. 18, 1961 "ice as mechanical support. The round waveguide 12 is surrounded by a coaxial wire coil 14 having its two terminals connected through a switch 16 to a source of direct current 17. One end of the round Waveguide 12 is terminated in a conductive end Wall pierced by a rectangular waveguide 18. By choice of dimensions the hollow rectangular waveguide 18 is matched in impedance at its junction with the dielectric-filled round waveguide 12. The round waveguide 12 constituting the outer wall of the polarization rotator is connected at its end opposite waveguide 18 to four rectangular waveguides 19, 20, 21 and 22. Alternatively, the round waveguide 12 of the rotator 11 may be joined through a length of round waveguide to the four waveguides19, 20, 21 and 22.

The four rectangular waveguide arms 19, 20, 21 and 22 are joined in a four-way H-plane orthogonal junction so that the arms 19 and 21 are collinear and the arms 20 and 22'are collinear. The axis of arms 19 and 21, the axis of arms 20 and 22, and the axis of the round waveguide 12 all intersect at a single point within the junction. The end of the round waveguide 12 which is opposite to that entered by Waveguide 18 is secured to the junction of the four arms 19, 20, 21 and 22 so that there is microwave energy communication from the rotator 11 to the four arms. The orientation of waveguide 18 is such that, if continued, it would form an E-plane or series T junction with the arms 19 and 21. The junction of the rotator and the four arms is matched by a button or post 23 secured to the wall of the junction opposite that entered by the rotator 11 and coaxial with the rotator.

The arms 20 and 22 are provided with short-circuiting conductive plugs 24 and 26 which may either be fixed or be adjustable as shown. In either case the distance from plug 24 to the point of axis intersection in the center of the junction is L and the distance from plug 26 to the same point is L plus an odd quarter wavelength of the microwave energy within the Waveguide, which may be defined as in which n is any positive integer including zero and A is the wavelength in the waveguide.

In the operation of this switch input power is applied to the rectangular waveguide 18 and the outputs are taken from the arms 19 and 21. The rotator 11 is so designed that when switch 16 is closed and the directcurrent source 17 has a selected strength, microwave energy entering the rotator from waveguide 18 is rotated through exactly 90 in its transit to the multiarm junction. Reflected energy entering the rotator from arms 20 and 22 will also be rotated 90 so that the quarter-turn'polarization will enable the energy to enter waveguide 18 without reflection or loss. 3

In operation to produce outputs at the arms 19 and 21 which are oppositely phased by exactly 180, and equal in amplitudes, the switch 16 is opened and the rotator 11 is left unenergized. Microwave energy in the TB dominant mode in waveguide 18 enters the rotator 11, and passes through without change of its direction of polarization: At the junction the energy is therefore presented to the arms 19 and 21 exactly as if applied from the stem of an E-plane (series) rectangular waveguide T .and is transmitted in two equal amounts, at opposite phases, out the arms 19 and 21.; The action is in all respects similar't'o-that in a series T. No energy can In operation to produce outputs atthe arms 19 and 21 which are identical in phase at equal distances from the junction, the switch 16 is closed, energizing the rotator 11. The direct-current source 17 and the magnetizing coil 14, as well as the design of the other parts of the rotator, are such that the microwave energy applied to the rotator from the waveguide 18 is rotated in polarization by 90. The direction of rotation is immaterial. -Microwave energy in the dominant or TE mode entering the rotator from the waveguide 18, being rotated 90, arrives at the junction with its polarization in suchdirection that it can enter the two arms Zt) and 22 in equal amounts and in opposite phases, as if the rotator together with the arms constituted a series T. The energy cannot now enter arms 19 and 21 directly. The energies are reflected from the short-circuiting plugs 24 and 26 back to the junction, and since the round-trip paths difler by one-half wavelength in the waveguide, the reflected energies are returned tothe junction in phase. They cannot reenter the round waveguide because it requires oppositely-phased feeds, but they can enter the arms 19 and 21, the action being analogous to that of a shunt T in which the arms 19 and 21 are analogous to the collinear arms of the T. The two energies from arms 20 and 22 combine by addition, and half of the sum is emitted from each of the arms 19 and :21, the phases being identical at equal distances from the junction along these arms.

This action is reciprocal, microwave energies applied in equal amounts and equal phases from the arms 19 and 21 combining to leave the rotator through the waveguide This invention thus provides means for an improvement in the operation of such systems by converting a phase discrepancy into an amplitude error.

What is claimed is: j 1. A phase reversing microwave switch comprising,

I four rectangular waveguide sections orthogonally joined 18, provided the switch'le is closed and the rotator is inoperation as described. output from waveguide 18 may have a phase reversed 180 from the phase in the case of energy applied, to waveguide 18, but such reversed-phase energy is transmitted equally well by the rectangular waveguide 18.

To sum up, when the rotator 11 is completely'deenergized the outputs from arms 19 and 21 are equal in amplitude and opposite in phase, and when the rotator 11 is energized to cause a rotation of exactly 90 the outputs from arms 19 and 21 are equal in amplitude and equal in phase.

An advantage of this invention is the opportunity it gives, when the polarizations applied by the rotator to the junction contain any selected angular error, to adjust the lengths L in both arms 26 and 22 in such manner as to translate the error into output relative phase error, or into output relative amplitude error, or into any mixture of these two kinds of error which may be desired.

As an exampre, let it be supposed that with the coil 14 unenergized, residual magnetism in the ferrite rod 13 causes a small rotation ofthe voltage vector as the microwave energy passes through the rotator 11; Most of the energy then passes outof arms 19 and 21 in opposite phase, but a small amount which is a function of the sine of the small rotation angle passes into arms 20 and 22, is'reflected, and passes out of arms '19 and 21 in.

In this reciprocal action the small quantity of energy in arm 19 is the same as the together at a common junction with broad sides thereof lying in a common plane providing two. pairs of collinearly disposed arms positioned in cruciform orientation, a round waveguide section joined to said rectangular waveguide sections at said common junction and extending in a direction normal to said common plane, reflective terminations for each of the arms of one pair of collinearly disposed arms, the distance from one of said reflective terminations to said common junction exceeding the distance between said common junction and the other reflective termination by an odd number of quarter wavelengths of energy in said waveguide sections, means for introducing linearly polarized energy into said round waveguide section with an orientation such that the E-vectors thereof extend in a direction parallel to the longitudinal axis of one ofthe pairs of collinearly disposed arms, and means for rotating the orientation of said linearly polarized energy through an angle of 2. A phase reversing microwave' switch comprising, four rectangular waveguide sections orthogonally joined together at a common junction with broad sides thereof lying in a common-plane providing two pairs of collinearly disposed arms positioned in cruciform orientation, a round waveguide section joined to said rectangular waveguide sections at said common junction and extending in -a direction normal to said common plane, reflective terminations for each of the arms of one pair of collinearly disposed arms, the distance from one of said reflective terminations to said common junction exceeding the distance between said common junction and the other reflective termination by an odd number of quarter wavelengths of energy in said waveguide sections, means for introducing linearly polarized energy into said round waveguidesection with an orientation such that the E-vectors thereof extend in a direction parallel to the longitudinal axis of one of the pairs of collinearly disposed.arms,- a body of gyromagnetic material 1 in saidround waveguide section, and means for selectively imposing a magnetic field of such a strength on said gyromagnetic material as to rotate the orientationof said linearly polarized energythrough an angle References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES fMeyer et at; fIRE Transactions on Microwave Theory Techniquesf-December 1 955, pages 43-44. 

